Recently, a bulky polyamide continuous multifilament yarn has been utilized in a tufted carpet, especially a cut pile carpet. In this case, when the bulky polyamide continuous multifilament yarn is used in a shaggy and saxony carpet, the bulky multifilament yarn which is obtained after a multifilament yarn receives a turbulent jet of heated fluid or a stuffing operation of fluid, generally receives additional twists between 30 T/m and 250 T/m, and then it is heat set by means of saturated steam, dry heat or the like so that the twists therein are set. Thereafter, the bulky yarn is utilized in a carpet as a pile yarn.
Such a bulky yarn obtained after twisting and heat setting has both preferable bulkiness adjusted by heat setting and suitable coherency caused by twisting. As a result, when the yarn is utilized in a cut pile carpet, the filaments of each cut pile gather together to form a slender shape like a pencil (this will be called a pin-point effect hereinafter), and the carpet has good quality. However, the cohesive bulky yarn obtained after twisting and heat setting has some problems. One of the problems is that the manufacturing cost of the yarn is high because the yarn requires two additional separate operations, i.e., twisting and heat setting. Another problem is that the yarn loses the above-mentioned pin-point effect and the hand and appearance thereof becomes felt-like after the cut pile carpet with pile yarns of the above-mentioned bulky yarn is utilized for a long duration because its coherency lowers gradually.
To eliminate the above-mentioned problems, methods have been attempted wherein the twisting and heat setting operations of the bulky yarn for carpet pile yarn are omitted and another method is carried out to impart coherency to the yarn. For example, in U.S. Pat. No. 3,611,698, a bulky yarn is entangled by means of a fluid flow so that a high degree of interlace is imparted therein. In U.S. Pat. No. 3,968,638, a bulky yarn is also false twisted by means of a fluid jet after it is interlaced so that latent twists are imparted therein. However, due to these methods, it is difficult to impart to a bulky polyamide multifilament yarn having a thick denier a uniform coherency along a lengthwise direction of the yarn by means of interlacing. In addition, highly entangling portions have an excessive coherency, and non-uniformity of dyeability or dyeing specks may occur. As a result, there is caused an additional problem in that the quality of a carpet is substantially degraded.
In accordance with the method disclosed in another U.S. Pat. No. 3,971,200, the pile yarn is maintained in a non-twisted situation. As a result, the yarn may split and filaments composing the yarn may be slack. Since the whole yarn does not have sufficient coherency, the operabilities, especially tufting operability, of the yarn are low.
The yarn disclosed in the above-mentioned U.S. Pat. No. 3,968,638 is not wholly as cohered as a true twisted yarn, and opened and entangled portions are alternately distributed along the yarn. In the opened portions of the yarn, splitting of the yarn and slacking may occur, and problems occur in that the yarn becomes entangled with machine parts or another yarn and the yarn is split by means of tufting needles while the yarn is being tufted.